Preparation of acrylic acid



Patented May 10, 1949 UNITED STATES ATENT OFFICE PREPARATION OF ACRYLICACID Bryan C. Redmon, Amherst, Mass., assignor to American CyanamidCompany, New York, N. Y., a corporation of Maine N Drawing. ApplicationFebruary 13, 1946, Serial No. 647,425

4 Claims.

The following specific examples, in which the proportions of reactantsare given in parts by weight unless otherwise indicated, are illustratedonly and it is not intended that the scope of the invention should berestricted to the details therein set forth.

Example 1 v Parts 85% phosphoric acid 68 Powdered copper metal 1l-lfydracrylic acid 250 The phosphoric acid and copper powder are placedin a suitably equipped vessel and dehydrated by heating under aprogressively decreased pressure until the temperature at 16 mm.pressure is 150 C.

With the above-prepared catalyst at a temperature of 150 C. and apressure of 50 mm., the hydracrylic acid is allowed to flow graduallyunder the surface of the hot catalyst. The catalyst mass begins to boilimmediately and a clear water-white liquid distills off. The distillinghead temperature slowly rises from 3738 C. to 78 C. at 50 mm. During thecourse of the run, the pressure is gradually decreased to 26 mm. and thecatalyst temperature increased to 170-180 C. Under these conditions, thedistilling head temperature varies from 65-80 C.

The rate of addition of the hydracrylic acid is regulated so that thetotal volume of catalyst in the reaction vessel remains as nearly thesame as possible. The total time consumed in adding the feed is about 1/2 hours at the rate of about 70-100 drops per minute.

227 parts, representing a 90.8% Weight recovery of the total hydracrylicacid feed, of a clear colorless liquid having a very strong, sharp odorare obtained. The weight loss as acrylic acid polymer and materialretained in the catalyst is 23 parts or 9.2% of the weight of the feed.

The clear colorless liquid has a 72.2% acrylic acid content, therefore163.9 parts of pure acrylic acid are produced. If it is assumed that thehydracrylic acid starting material is 100% pure, the yield of acrylicacid therefrom is 82%. It is more accurate, however, to calculate theyield of acrylic acid from the weight of the ethylene cyanohydrin whichwas used in the preparation of the hydracrylic acid according to theprocess of copending application Serial No. 462,050 filed October 14,1942, now abandoned, and Patent No. 2,369,491 dated February 13, 1945.This is 77.4%.

Pure acrylic acid is separated from the 72.2% aqueous solution byfractional distillation at reduced pressures. The following fractionscomprise the pure acid:

Pressure, mm. Eg. p i i t j O.

Example 2 Parts phosphoric acid 49 Copper powder 2 Hydracrylic acid 568mm. and the hydracrylic acid is allowed to drip slowly under the surfaceof the heated catalyst. The distilling head temperature rises rapidly,remains at 8090 C. for the major part of the run, and then rises almostto C. at the end. A pressure of 40 mm. is held for the major part of therun but it is decreased to 30 mm. toward the end. The temperature of thecatalyst is held at -190 C. throughout the run. The total time consumedin adding the hydracrylic acid is about 4 hours at the rate of 70-120drops per minute. The product is collected at about the same rate.

The product is 510 parts of a clear, colorless liquid which correspondsto 89.6% of the weight of the hydracylic acid. The liquid is 77% acrylicacid, representing a yield of 392.7 parts pure acid or 86.4% based on100% pure hydracrylic acid. This figure corresponds to a yield of 76%based on the ethylene cyanohydrin from which the hydracrylic acid may beprepared.

Example 3 Parts 95% sulfuric acid 300 Powdered metallic copper 5Hydracrylic acid 1581 The mixture of sulfuric acid and copper is placedin a suitably equipped vessel and heated to 141 C. The pressure is thenreduced to 35 mm. and the hydracrylic acid is allowed to drip below thesurface of the heated catalyst.

Shortly after the beginning of the reaction, the pressure is decreasedto 25 mm. and is held at 23-26 mm. throughout the run. The temperatureof the catalyst is held at 125135 C. during the first half of the runand raised to 140-150 C. during the last half.

A total of about hours is required for addition of all the hydracrylicacid at the rate of 400-500 cc. per hour for about 3 /2 hours and200-300 cc. per hour for the remaining period of time.

1264.5 parts of clear, colorless liquid product, equivalent to 80% ofthe total weight of the feed, is obtained. The product is 81.4% acrylicacid or 1029.3 parts of the pure acid, a yield from assumed 100% purehydracrylic acid of 81.3% and from ethylene cyanohydrin 76.1%.

The hydracrylic acid used as starting material in the preceding examplesWas obtained from ethylene cyanohydrin according to the processdisclosed and claimed in Patent No. 2,369,491 issued February 13, 1945,and copending application Serial No. 462,950 filed October 14-, 1942,but hydracrylic acid from any other source may be used in the process ofthe invention.

Dehydration catalysts other than phosphoric and sulfuric acids may beused. For example, boric acid, zinc chloride, benzene sulfonic acid, andp-toluene sulfonic acid are equally as effective. Similarly, the copperpowder may be replaced by other polymerization inhibitors such as bronzepowder, chromium, manganous salts, hydroquinone, catechol, ferricsulfate, etc., without departing from the spiirt of the invention.

The dehydration reaction is carried out below 40 atmospheric pressure toavoid polymer formation and thereby provide good yields of acrylic acid.Pressures below 100 mm. of Hg and especially around 20-60 mm. of Hg arepreferred.

The dehydration temperature giving best results will vary somewhat withthe particular catalyst employed, but in general I have found itadvantageous to carry out the reaction at temperatures of between about130 C. and 190 C.

It is an advantage of the present invention that hydracrylic acid may becontinuously dehydrated to produce good yields of acrylic acid.Moreover, the water-white product obtained which contains no impurityother than about 20% water may be used for many purposes without furtherpurification.

I claim:

1. In the process of preparing acrylic acid by dehydration ofhydracrylic acid, the steps which comprise adding the hydracrylic acidgradually to an acid dehydration catalyst maintained at dehydrationtemperatures of between about 130 to 190 C. under pressures below 100mm. of Hg to form an aqueous solution of acrylic acid and distilling ofithe aqueous acrylic acid as formed, the .rate of addition of hydracrylicacid being so regulated that the total volume of catalyst remains nearlyconstant.

2. In the process of preparing acrylic acid by dehydration ofhydracrylic acid, the steps which comprise adding the hydracrylic acidgradually to an acid dehydration catalyst maintained at dehydrationtemperatures of between about to 190 C. under pressures below 100 mm. ofHg to form an aqueous solution of acrylic acid, distilling off theaqueous acrylic acid as formed, the rate of addition of hydracrylic acidbeing so regulated that the total volume of catalyst remains nearlyconstant, and recovering pure acrylic acid from the aqueous solutionthereof by fractional distillation at reduced pressures.

3. The process of preparing acrylic acid which comprises addinghydracrylic acid gradually to concentrated phosphoric acid maintained ata temperature of about 150-190 C. and a pressure of about 26-50 mm. ofHg in the presence of powdered metallic copper and separating theaqueous acrylic acid formed from the catalyst by distillation.

4- The process of preparing acrylic acid which comprises heating amixture of concentrated sulfuric acid and powdered metallic copper toabout C., reducing the pressure to about 35 mm. of Hg, gradually addinghydracrylic acid, controlling the temperature and pressure throughoutthe addition so the temperature remains between 125 C. and C. and thepressure between 23 mm. and 26 mm. of Hg, and separating the aqueousacrylic acid formed from the catalyst by distillation.

BRYAN C. REDMON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,026,894 Hill Jan. 7, 19362,174,830 McAllister et al Oct. 3, 1939 2,305,663 Beer et a1. Dec. 22,1942 2,341,663 Schulz Feb. 15, 1944 2,356,247 Kirk et al Aug. 22, 19442,361,036 Kung Oct. 24, 1944 2,374,051 Spence Apr. 17, 1945 FOREIGNPATENTS Number Country Date 427,810 Great Britain Oct. 4, 1934 455,087Great Britain Oct. 13, 1936 OTHER REFERENCES Moldenhauer, Wislicenus,Beilstein (4th ed.), (1864).

Wislicenus, Liebigs Ann., vol. 166, pages 23-25 (1873).

Erlenmeyer, Liebigs Annalen, vol. 191, pp. 261- 284 (1878).

Moldenhau-re, Wislicenus, Beilstein (4th ed.), Vol.3, page 296 (.1921).

Van der Burg, Rec. Trav. Chim., vol. 41, pp. 22-23 (1922').

